add intro block

Author: sgratzl

README.md

@@ -1,6 +1,21 @@
 # D3 Tutorial
 
-This is a short tutorial introducing the basic elements and concepts of D3. D3 stands for Data-Driven Documents and is a very popular JavaScript library written by [Mike Bostock](https://bost.ocks.org/mike/).
+This is a short interactive tutorial introducing the basic elements and concepts of D3. At the beginning of this tutorial the foundations of D3 namely HTML, CSS, SVG, and JavaScript are briefly explained.
+
+Then, the basic principles of D3 and its functions are introduced by incrementally implementing an interactive bar chart.
+The example can be implemented manually or directly by editing the [CodePen](https://codepen.io) examples.
+
+In the second part of this tutorial a more complex multiple coordinated view (MCV) setup is incrementally implemented. A multiple coordinated view setup consists of multiple visualizations that are interactivly linked together such
+as selecting an element in one visualization filters the data in a second one. This is also called linking and brushing. Along with this example some guidelines
+regarding code structure and advanced D3 transitions are given.
+
+This tutorial concludes with a brief introduction into other visualization libraries and hints about how to use D3 with [TypeScript](https://www.typescriptlang.org/).
+
+Now, shall we begin...
+
+---
+
+D3 stands for Data-Driven Documents and is a very popular JavaScript library written by [Mike Bostock](https://bost.ocks.org/mike/).
 
 Homepage: https://d3js.org/
 
@@ -1157,7 +1172,7 @@ One can specify the type in more detail by specifing the generic argument of the
 
 ---
 
-Barchart final results in TypeScript [barchart07_final_ts.html](examples/barchart07_final_ts.html) [![Open in CodePen][codepen]](https://codepen.io/sgratzl/pen/gObqdEG)
+Barchart final results in TypeScript [barchart07_final_ts.ts](examples/barchart07_final_ts.ts) [![Open in CodePen][codepen]](https://codepen.io/sgratzl/pen/gObqdEG)
 
 ### Hints